A compound contains 29% Na by mass. If the only other element present is Cl, what is the empirical formula of the compound?

• A. NaCl2
• B. NaCl
• C. Na2Cl2
• D. Na2Cl

Answer: (B)

Verified step by step guidance

1. Identify the mass percentages of each element in the compound. Given that the compound contains 29% Na by mass, the remaining percentage must be Cl, which is 100% - 29% = 71%.
2. Convert the mass percentages to moles by dividing each element's mass percentage by its atomic mass. Use the atomic masses: Na = 22.99 g/mol and Cl = 35.45 g/mol. Calculate moles of Na as \(\frac{29}{22.99}\) and moles of Cl as \(\frac{71}{35.45}\).
3. Determine the simplest whole number mole ratio by dividing both mole values by the smaller of the two mole amounts. This step normalizes the ratio to the smallest whole numbers.
4. If the mole ratio is not a whole number, multiply both ratios by the smallest integer that converts them into whole numbers. This gives the subscripts for the empirical formula.
5. Write the empirical formula using the mole ratio as subscripts for Na and Cl. For example, if the ratio is approximately 1:1, the empirical formula is NaCl.